1. Field of the Invention
The present invention relates to a process for the preparation of .omega.-enecarboxylic acid esters by hydrocarboxyalkylation of .alpha.,.omega.-dienes.
2. Discussion of the Background
In the context of the present invention, .omega.-enecarboxylic acid esters are compounds which possess a terminal carbon-carbon double bond at one end of an alkylene chain and an ester group at the other end of the alkylene chain.
.omega.-Enecarboxylic acid esters are valuable intermediates for the production of detergents, lubricants, emulsifiers, plasticizers, alkyd resins, polyamides, and perfumes and flavors.
.omega.-Enecarboxylic acids with up to 13 carbon atoms can be synthesized from small structural units in several steps by the method of A. Seher, Fette-Seifen-Anstrichmittel, 58, 1077 (1956). .omega.-Enecarboxylic acids can be produced from .omega.-eneketocarboxylic acids by Wolff-Kishner reduction according to the method of S. Huenig and W. Eckardt, Chemische Berichte, 95, 2498 (1962). The starting materials for this reaction are not available in industrial quantities. Furthermore, the double bond is partly isomerized during the reduction. Neither method has attained industrial importance.
According to DE-A 36 09 138 and DE-A 36 09 139, .omega.-enecarboxylic acid esters with chains of 5 to 7 carbon atoms can be obtained by cleaving lactones. In this method, which is suitable only for preparing short-chained .omega.-enecarboxylic acid esters, the double bond is partly isomerized. Because of this isomerization, products with an internal double bond are also synthesized in substantial quantities.
According to DE-A 30 24 884, unsaturated C.sub.9 -carboxylic acids can be prepared by carboxylative dimerization of 1,3-butadiene with carbon dioxide in the presence of palladium compounds, phosphine, and formic acid. However, the 2-ethylidenehept-6-enecarboxylic acid obtained in the mixture has both a terminal and an internal double bond and a branch.
Olefins can be hydrocarboxyalkylated with carbon monoxide in the presence of alcohols by the method of J. Falbe, Synthesen mit Kohlenmonoxid, 102 (1967). Thus, unsaturated monocarboxylic acid esters can be prepared from 1,5-cyclooctadiene on Pd/HCl, while the saturated monocarboxylic acids are always formed on cobalt catalysts. 1,5-Hexadiene reacts with cyclization on a palladium catalyst.
No process for the hydrocarboxyalkylation of .alpha.,.omega.-dienes with the formation of .omega.-enecarboxylic acid esters is described by J. Falbe.
Thus, there is a need for a process to prepare .omega.-enecarboxylic acid esters from economical, simple starting compounds which are available in large quantities.
In particular, there is a need for a process to prepare largely unbranched .omega.-enecarboxylic acid esters from readily available starting materials.